Custom fresnel curve
Here is the Fresnel Conductive OSL node done in pure Cycles nodes:



The node noodles:



And .blend with linkable/apendable group if you feel lazy to build this:)





Notes:

In reality the IOR is computed like this:

IOR = N + Ki

where N is Refractive index and K is Extinction coefficient. For dielectrics, the complex part can be omitted, so N becomes the IOR. However metals do have the complex part.

You get the measured N and K values from here: https://refractiveindex.info/. The problem is, that both N and K depend on the wavelength of light.

So to render metals correctly, Cycles would have to be a spectral renderer taking into account the polarization and wavelength of light.

The best we can do is to approximate and sample just for red, green and blue light.

As per the Vray OSL reference the red, green and blue values are taken at 0.65, 0.55 and 0.45 micrometers. Put the wavelength value in there and read N and K:



The usage is same as in Scott Milner's answer. This is how the Conductive's Fresnel output can look like (with extreme values):



You can see it produces the Reflectivity color and Edge Tint color that you would normally input in an artistic-driven metal shader.  But this is from exact measured values and with correct math so the way the colors blend towards the edge is more accurate than using an artistic metal shader with hacked (usually just adjusted for the base reflectance) fresnel node (which in Cycles gives dielectric reflectance response curve).

Connect this into Glossy shader color. The shader should have 0 roughness to be correct.



[UPDATE]: As roughness increases, rays have higher probability to hit the surface dead-on as in center of the sphere. When roughness reaches 1, the whole sphere is shaded with the reflectivity color:



Here is an upgraded PBR version with roughness all incorporated into one group:



Node group guts:



Blend file:



Now this approach taking measured N and K values has GPU and roughness support - two biggest downfalls removed - which imho puts it on par with PBR artistic-driven shader setups:


artistic approach with reflectance and edge-tint color input has ease of adjustment benefit (you can also find recommended/measured color values for metals online).
measured N and K values approach gives better and more accurate reflectance behaviour (but still approximated in non spectral renderers).